The diffusion of Cu into undoped material reduced the concentration of the EL6 and EL2 deep-donors and created a deep-donor level at about 0.66eV, in addition to the well-known acceptor levels at 0.15 and 0.44eV; as revealed by deep-level transient spectroscopic and temperature-dependent Hall measurements. An analysis which was based upon these observations, and a charge-balance equation, was carried out in order to understand the compensation process at various stages. The possible identity of the deep-donor which was responsible for the semi-insulating properties was considered, as was the anomalous transport behavior in the highly-compensated samples.

B.H.Yang, H.P.Gislason: Materials Science Forum, 1995, 196-201, 713-8